Incoherently beam combined (IBC) lasers combine the output from an array of gain elements or emitters (typically consisting of semiconductor material, such as GaAlAs, GaAs, InGaAs, InGaAsP, AlGaInAs, and/or the like, which is capable of lasing at particular wavelengths) into a single output beam that may be coupled into, for example, an optical fiber. The gain elements may be discrete devices or may be included on an integrated device. Due to the geometry of IBC lasers, each gain element lases a particular wavelength. Exemplary arrangements of IBC lasers are described in U.S. Pat. No. 6,052,394 and U.S. Pat. No. 6,192,062.
FIG. 8 depicts a prior art arrangement of components in IBC laser 80. IBC laser includes emitters 82-1 through 82-N associated with fully reflective surface 81 and front surface 84. Emitters 82-1 through 82-N are disposed in a substantially linear configuration that is roughly perpendicular to the optical axis of collimator 85 (e.g., a lens). Collimator 85 causes the plurality of beams produced by emitters 82-1 through 82-N to be substantially collimated and spatially overlapped on a single spot on diffraction grating 86. Additionally, collimator 85 directs feedback from partially reflective component 87 via diffraction grating 86 to emitters 82-1 through 82-N.
Diffraction grating 86 is disposed from collimator 85 at a distance approximately equal to the focal length of collimator 85. Furthermore, diffraction grating 86 is oriented to cause the output beams from emitters 82-1 through 82-N to be diffracted on the first order toward partially reflective component 87. Partially reflective component 87 causes a portion of optical energy to be reflected. The reflected optical energy is redirected by diffraction grating 86 and collimator 85 to the respective emitters 82-1 through 82-N. Diffraction grating 86 angularly separates the reflected optical beams causing a particular wavelength generated by each emitter 82-1 through 82-N to return to each respective emitter 82-1 through 82-N. Accordingly, diffraction grating 86 is operable to demultiplex the reflected beams from reflective component 87.
It shall be appreciated that the geometry of external cavity 83 of IBC laser 80 defines the resonant wavelengths of emitters 82-1 through 82-N. The center wavelength (λi) of the wavelengths fed back to the ith emitter 82-i is given by the following equation: λi=A[sin(αi)+sin(β)]. In this equation, A is the spacing between rulings on diffraction grating 86, αi is the angle of incidence of the light from the ith emitter on diffraction grating 86, and β is the output angle on diffraction grating 86 which is common to all emitters 82-1 through 82-N. As examples, similar types of laser configurations are also discussed in U.S. Pat. No. 6,208,679.